The invention relates to new photosensitive optically variable (POV) inks, and more particularly, to water soluble POV inks capable of printing images having enhanced functionality making them well adapted for use as security inks.
The POV inks of the invention are effective for use with inkjet printing and have a range of security applications. They can produce security markings of a type which set them apart from other inks. While POV inks present a significant challenge to counterfeiting when available from a secure source or licensed supplier, even the most sophisticated security measures can sometimes be circumvented. The invention provides inkjet inks having security features that are not easily detectable in the first instance and not readily reproduced once detected.
The inks of the invention are photosensitive optically variable, meaning that they can provide a printed visually black or dark gray machine-readable information-bearing marking that fluoresces in a specific wavelength range when excited with a shorter wavelength light. The printed images exhibit visual light absorption throughout the entire visual spectrum including the red region of the visible spectrum where red inks are invisible to typical automatic scanning systems. Inks of this type are described, for example by U.S. Patent Publication No. 2003/0041774, U.S. Patent Publication No. 2002/0195586, and commonly-assigned, copending U.S. patent application Ser. No. entitled, Photosensitive Optically Variable Ink Compositions Useful for Ink Jet Printing, filed on equal date with this application, in the names of J. D. Auslander and M. Chen. These inks will achieve acceptable PCS (Print Contrast Signal) on virtually all conventional substrates, including dark papers such as Kraft or Manila. The term PCS refers to the ratio of the Print Reflectance Difference (PRD) and the substrate reflectance, and the PRD is the difference between the paper reflectance and ink reflectance. These and other postal terms are given their meanings as defined by the United States Postal Service (USPS). These inks can be used with automated detectors of various types of information-bearing tickets, tags, labels, postage indicia and similar security markings.
There are many reasons for simply and effectively identifying the sender or originator of mail or other transported items, and there is a need for very high security to justify a high level of trust. In the case of mail, the use of Sender Identified Mail (SIM) markings is effective to help sort mail and can be used to verify rates and other information. Where security is important, the use of POV inks can provide a useful added layer of security. It would be desirable to have inks which appeared to be POV inks of the type described above, but which had an additional and not easily detectable security feature. Inks of this type could be of especial value where they are available from controlled sources and, especially, when used with a security method correlating formulation with authorized users. Such inks could enable a mail sorting facility to rapidly screen large volumes of mailpieces from trusted senders, thereby reducing or eliminating the need to specially handle every piece of mail for security screening.
The term “fluorescent security marking”, as used herein, refers to a security marking that fluoresces in a defined region of the spectrum upon exposure to a shorter wavelength excitation light, such as UV light. The shift in wavelength between the incident excitation light and the fluorescent emission clearly distinguishes fluorescence from direct reflection. While the above POV inks can provide fluorescent security markings that are coincident with visible images, making them very difficult to detect and copy, especially where the inks are subject to controls restricting their availability, there is a need to address the challenge of making such inks even more difficult to counterfeit and capable of providing unique “fingerprints” suitable for forensic tracing. The invention adds an additional layer of security, making them phosphoresce—providing a lingering, detectable characterizing emission.
Automated detectors are known that are responsive to reflected visible light and fluorescent emissions from security markings resulting from excitation at a shorter wavelength, such as ultraviolet (UV) excitation. These inks can be used by detectors to verify that the fluorescence and the indicium image are physically coincident. They are also capable of inkjet printing for the provision of easily variable information. They form a very small class adapted for fluorescent security marking that can be implemented with high speed on a wide variety of substrates to provide easily variable security markings capable of high speed verification. Detectors currently in use in high speed facer/canceller machines can read FIM's and detect red fluorescence in postage marks and green phosphorescence in stamps. There is currently no assigned function for red phosphorescence and there are no security POV inks possessing such a characteristic.
There is a need for additional POV inks that provide effective security, with unique compositions to yet further enhance the provision of security systems having customizable and traceable properties.